The invention relates to processes and devices for disintegrating irregularities in flow of wood fibers that are discharged from a metering device and designated for the production of fiberboards.
When producing MDF or HDF boards, if the fibers are glued in a wet state, the consumption of glue is relatively high because part of the reactivity of the glue is lost during the drying process of the fibers due to the high temperatures. Consequently, the emission of formaldehyde, originating from the glue, is considerable in the drying system, thus necessitating a costly minimizing of harmful substances.
If the fibers are not glued in gluing machines until after the drying process, it is possible to reduce the glue consumption and the emission of formaldehyde, however, bundles of fibers, drops of condensed water or lumps of glue are created in the fiber flow, in this so-called “dry-gluing process” or “mechanical gluing”. Such irregularities in the fiber flow, which also occur Tao lesser extent when gluing in the wet state, lead to defects in the finished board and therefore can result in rejects.
In order to cover these defective areas, it is known, to glue the fibers of outer layers of fiberboards to be produced while wet and fibers of inner layers in a dry state. This, however, makes the production of fiberboards expensive.
It is also known from general practice to use a hammer mill to break up lumps of fibers that have formed, for example, due to condensed water. Such a hammer mill, however, rapidly becomes soiled and is not very effective.
Rollers, which can be used to disintegrate irregularities in a fiber flow are known per se from DE 38 18 117 A1, DE 44 39 653 A1 and from WO 99/11441. However, the effectiveness of these rollers is limited with respect to disintegrating irregularities.
EP 0 800 901 A1 describes a device for producing a mat in particular from chips where rollers are provided which in conjunction with a downstream air sifter are used to separate the chips based on their size, in order to achieve a distribution of sizes over the mat thickness. In the case of particulate material in the form of fibers it is not possible to achieve a satisfactory disintegrating effect using such rollers. In the case of fiberboards, owing to the desired homogeneity in the structural constitution there is no desire to separate the fibers into different size particles.
DE 43 02 850 C2 describes a generic process and a generic device. The compacted particulate material is disintegrated by means of two rollers which are rotating in opposite directions at different speeds and which grip into each other and as a consequence comprise disintegration teeth which form a serpent-like splitting space. A plurality of distributing rollers are provided downstream for the purpose of distributing the fibers. However, this process is extremely costly.
The object of the invention is to provide a generic process which is extremely effective and not very expensive. Moreover, the object of the invention is to provide a generic device with which such a process can be performed.